1. Field of the Invention
The present invention relates to a droplet ejecting apparatus and a droplet ejecting method, particularly to the droplet ejecting apparatus and droplet ejecting method for ejecting a droplet based on an applied voltage.
2. Description of the Related Art
Conventionally, in a droplet ejecting head in which an electromechanical transducer such as a piezoactuator is used, a pressure change is generated in a pressure chamber to eject a droplet by applying a voltage to the electromechanical transducer.
Because the state of generation of satellite drops and mist is changed by a reverberation pressure change in the pressure chamber after a droplet is ejected by the applied voltage, satellite drops and mist are generated, which causes degradation of image quality and a decrease in apparatus reliability, unless the reverberation pressure change is appropriately set. That is, when flight speed of the satellite drops is slow, a large difference in landing position is generated between the satellite drops and the droplets ejected by the applied voltage waveform, which causes problems that the image quality deteriorates and droplet ejection failure is generated.
Japanese Patent Application Laid-Open (JP-A) No. 59-176060 discloses an inkjet head driving method of suppressing the generation of satellite drops and mist. In the method disclosed in JP-A No. 59-176060, ink droplets are ejected by applying a main driving signal to a piezoelectric element, and a driving signal having a reverse phase is applied to a natural oscillation excited in association with the ink droplet ejection. Japanese Patent Application Laid-Open (JP-A) No. 2000-280463 and No. 2003-276200 disclose methods of driving an ink ejection apparatus. In the methods disclosed in JP-A No. 2000-280463 and 2003-276200, a non-ejecting pulse is applied so as to suppress remaining pressure wave vibrations generated by the ejecting pulse in an ink channel after the ink droplet ejection.
In the inkjet driving method disclosed in JP-A No. 59-176060 and the method of driving the ink ejection apparatus disclosed in JP-A No. 2000-280463 or 2003-276200, when a liquid having large viscosity is ejected, because an attenuation constant of the pressure change is increased, the reverberation pressure change is attenuated rapidly immediately after the ink droplet is ejected, and an appropriate amount of reverberation for preventing satellite drops and mist cannot be obtained. That is, because reverberation becomes too little immediately after the ink droplet is ejected, the ink droplet is slowly separated from the meniscus, and the methods are susceptible to low-speed satellite drops and mist generation.